java.util
Class HashSet<T>
- Implemented Interfaces:
- Cloneable, Collection<E>, Iterable<E>, Serializable, Set<E>
- Known Direct Subclasses:
- JobStateReasons, LinkedHashSet<T>
This class provides a HashMap-backed implementation of the Set interface.
Most operations are O(1), assuming no hash collisions. In the worst
case (where all hashes collide), operations are O(n). Setting the
initial capacity too low will force many resizing operations, but
setting the initial capacity too high (or loadfactor too low) leads
to wasted memory and slower iteration.
HashSet accepts the null key and null values. It is not synchronized,
so if you need multi-threaded access, consider using:
Set s = Collections.synchronizedSet(new HashSet(...));
The iterators are
fail-fast, meaning that any structural
modification, except for
remove() called on the iterator
itself, cause the iterator to throw a
ConcurrentModificationException rather than exhibit
non-deterministic behavior.
Constructor Summary
HashSet()- Construct a new, empty HashSet whose backing HashMap has the default
capacity (11) and loadFacor (0.75).
HashSet(T> c)- Construct a new HashSet with the same elements as are in the supplied
collection (eliminating any duplicates, of course).
HashSet(int initialCapacity)- Construct a new, empty HashSet whose backing HashMap has the supplied
capacity and the default load factor (0.75).
HashSet(int initialCapacity, float loadFactor)- Construct a new, empty HashSet whose backing HashMap has the supplied
capacity and load factor.
Method Summary
boolean add(T o)- Adds the given Object to the set if it is not already in the Set.
void clear()- Empties this Set of all elements; this takes constant time.
boolean contains(Object o)- Returns true if the supplied element is in this Set.
boolean isEmpty()- Returns true if this set has no elements in it.
Iterator iterator()- Returns an Iterator over the elements of this Set, which visits the
elements in no particular order.
boolean remove(Object o)- Removes the supplied Object from this Set if it is in the Set.
int size()- Returns the number of elements in this Set (its cardinality).
T[] toArray,
add,
addAll,
clear,
contains,
containsAll,
isEmpty,
iterator,
remove,
removeAll,
retainAll,
size,
toArray,
toString
Methods inherited from class java.lang.Object
clone,
equals,
extends Object> getClass,
finalize,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait
Constructor Details
HashSet
public HashSet()
Construct a new, empty HashSet whose backing HashMap has the default
capacity (11) and loadFacor (0.75).
HashSet
public HashSet(T> c)
Construct a new HashSet with the same elements as are in the supplied
collection (eliminating any duplicates, of course). The backing storage
has twice the size of the collection, or the default size of 11,
whichever is greater; and the default load factor (0.75).
- Parameters:
c - a collection of initial set elements
HashSet
public HashSet(int initialCapacity)
Construct a new, empty HashSet whose backing HashMap has the supplied
capacity and the default load factor (0.75).
- Parameters:
initialCapacity - the initial capacity of the backing HashMap
HashSet
public HashSet(int initialCapacity,
float loadFactor)
Construct a new, empty HashSet whose backing HashMap has the supplied
capacity and load factor.
- Parameters:
initialCapacity - the initial capacity of the backing HashMaploadFactor - the load factor of the backing HashMap
Method Details
add
public boolean add(T o)
Adds the given Object to the set if it is not already in the Set.
This set permits a null element.
- Parameters:
o - the Object to add to this Set
- Returns:
- true if the set did not already contain o
clone
public Object clone()
Returns a shallow copy of this Set. The Set itself is cloned; its
elements are not.
- Overrides:
- clone in interface Object
- Returns:
- a shallow clone of the set
iterator
public Iterator iterator()
Returns an Iterator over the elements of this Set, which visits the
elements in no particular order. For this class, the Iterator allows
removal of elements. The iterator is fail-fast, and will throw a
ConcurrentModificationException if the set is modified externally.
- Specified by:
- iterator in interface Set<E>
- iterator in interface Collection<E>
- iterator in interface Iterable<E>
- Overrides:
- iterator in interface AbstractCollection<E>
HashSet.java -- a class providing a HashMap-backed Set
Copyright (C) 1998, 1999, 2001, 2004, 2005 Free Software Foundation, Inc.
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